Fluorine-containing polymers, or fluoropolymers, including fluoroelastomers and fluoroplastics, are an important class of commercial materials. Fluoropolymers are known to exhibit chemical inertness (resistance to chemical attack), high thermal stability, usefulness at high temperatures, and toughness and flexibility at very low temperatures.
Useful fluoropolymers include fluoroelastomers and fluoroplastics. Usefull fluoroelastomers can contain interpolymerized units derived from olefinically unsaturated monomers, such as monomers of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, etc. These fluoroelastomers have particular utility in high temperature applications, such as seal gaskets and linings. Fluoroplastics, particularly those containing interpolymerized monomeric units derived from chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, have numerous electrical, mechanical, and chemical applications. As an example, these fluoroplastics are useful in wire, electrical components, seals, solid and lined pipes, and pyroelectric detectors.
Because fluoropolymers are often expensive, these materials are often used in the form of a composite, multi-layer structure which reduces the amount of fluoropolymer required to produce the structure. In the manufacture of these composite structures, may be required that the fluoropolymer be bonded to one or more hydrocarbon-based substrate that may or may not be fluorinated. Thus, the fluorinated and the hydrocarbon layers are combined, taking advantage of the useful properties of each type of material; i.e., the fluorinated layer can be a thin, flexible layer of material which provides resistance to chemical attack and/or vapor barrier properties, while the hydrocarbon substrate layer can provide desired strength and/or flexibility, and substantial cost reduction.
A variety of methods have been used to increase the bond strength between a fluorinated polymer layer and a hydrocarbon substrate layer such as a polyamide or polyolefin layer. For example, an adhesive layer can be added between the two layers. A shortcoming of adding an adhesive layer is that this increases the complication of the manufacturing process, due to the added step of applying the adhesive. Alternatively, one or both of the fluorinated or hydrocarbon layers can be exposed to various surface treatments; i.e., corona, flame, or plasma discharge treatment. A shortcoming of these types of surface treatment is that they can often be temporary and over time delamination of the product may occur during use.
Adhesive bond strength between a fluoropolymer and a hydrocarbon substrate can also be increased by chemical modification of the fluoropolymer or the hydrocarbon substrate; i.e., the addition of adhesion-promoting grafted substituents to one or more of the fluoropolymer or hydrocarbon substrate. For instance, in the case of the fluoropolymer, it can be reacted with an amine, a hydroxyl group, a free radical graft, etc., to produce a fluoropolymer comprising a grafted substituent that is reactive with the hydrocarbon substrate. Although such adhesion-increasing substituents can in fact result in improved adhesion between the fluoropolymer and a hydrocarbon substrate, the grafted substituents (on either the fluoropolymer or the hydrocarbon substrate) can also have undesired effects on the physical properties of the fluoropolymer or hydrocarbon substrate. By modifying the fluoropolymer, for example, with the addition of adhesion-promoting groups, the concentration of fluorine atoms on the fluoropolymer is reduced. As a result the chemical inertness of the fluoropolymer, and its ability to resist chemical attack, may be negatively affected. Additionally, important physical and/or mechanical properties of a fluoropolymer or of a hydrocarbon substrate, including melting point, glass transition temperature, and/or solubility, might be affected by the addition of adhesion-promoting groups. These changes in the chemical inertness and/or physical and mechanical properties can negatively and significantly affect the end properties of articles prepared from these modified fluoropolymers and/or hydrocarbon substrates, and are preferably avoided. Thus it would be useful to provide a method of creating or enhancing an adhesive bond between a fluoropolymer and a hydrocarbon substrate, without the addition of grafted, adhesion-promoting groups to the fluoropolymer or the hydrocarbon substrate.